It is known to supply a constant fresh air volume flow into the pressurized body of passenger aircraft on the ground and in the air for ventilating the passenger cabin, the cockpit, the electronics room and the cargo space. The air quality is maintained particularly in the cabin and in the cockpit by a constant volume air flow. In order to maintain the temperature and the air flow velocity of the ventilation air at a comfort level for the passengers and crew in the aircraft, a constant air volume in the form of a so-called recirculation air volume is admixed to the fresh air. The recirculation air is a small proportion of used cabin air. For this purpose the fresh air treatment facilities or so-called "climate packs" and the flow control valves (FCV) are controlled in closed loop fashion in accordance with the constant volume flow also referred to as bleed air. Only fault situations can cause a variation in the normally constant volume flows. Exceptions involve an additional air requirement for ventilating a cargo hold and for a so-called "economy mode" of operation for the cabin. Under these exceptions the air flow is adjusted to another value which, however, also becomes a constant value after adjustment. Thus, the conventional teachings make possible substantially only the switching between an economy mode, a normal mode, and a maximum mode, each having a constant air flow.
The conventional air conditioning in an aircraft is controlled in closed loop fashion so that the temperature in the cabin and in the cockpit is controlled in response to the outlet temperature of the climate pack or packs and by the so-called trim system. The outlet temperature of the climate pack or packs is used for adjusting the lowest temperature of all required air temperatures. The temperatures for zones requiring a higher temperature are controlled in closed loop fashion by admixing hot trim air from the engines.
Conventionally, it is a disadvantage that a high proportion of the used cabin air is not treated for reuse because the ventilation of the pressurized aircraft body is dependent on an open loop and closed loop control of the air volume flow in accordance with constant air flows, namely a constant volume fresh air flow and a constant volume recirculation air flow to be treated. Fresh air is conventionally not supplied with a view to merely compensating for leakage. Rather, the fresh air supply is intended to provide a sufficient ventilating of the pressurized aircraft body with a high proportion of fresh air, whereby the entire energy consumption or rather the fuel consumption of the system is correspondingly strained.
The closed loop pressure control in the pressurized aircraft body is conventionally performed disadvantageously independently of the fresh air volume and temperature control, whereby, the air flow which leaves the pressurized aircraft body, serves as a closed loop control value. If the pressure in the pressurized body rises, the air flow volume is increased. If the pressure falls, the air flow volume is correspondingly reduced in conventional systems.
The quality of the cabin air in a passenger and crew area, namely the cabin and the cockpit, is conventionally assured only by the constant fresh air flow of external air, whereby the required fresh air volume supply corresponds functionally to the required cabin air quality in the mentioned areas. The small proportion of used cabin air is passed through a particle filter and then added as recirculation air to the separately supplied fresh air for the ventilation. In conventional systems the recirculation air or used cabin air which is merely cleaned by a particle filter, but not treated in such a way that the recirculation air has fresh air quality, is a source of problems. Especially, if conventionally there is a significant increase in the used air proportion of the recirculating venting air, a very unfavorable effect on the well being of all passengers and crew members is observed because the recirculating air is insufficiently and poorly filtered, nor is it freed of disease carriers, for example bacteria and viruses which are present in the used air and which remain in the recirculated air. Additionally, the used air carries odor causing elements emanating from humans and food-stuffs. These components in the used air are substantially influenced by the people on board. In fact, the people on board substantially generate these components. Thus, it is conventionally undesirable to recirculate large proportions of used air. Conventional filter devices installed on board of aircraft do not satisfy current requirements where a significant increase of the used air proportion in the ventilating air is involved. Thus, conventional filtering devices cannot eliminate these conditions that are uncomfortable for passengers and crew.
Furthermore, the carbon dioxide proportion in the cabin air significantly and adversely influences the air quality. Without an adsorption of CO.sub.2 the carbon dioxide proportion rises to unpermissably high values if a significant proportion of the recirculating ventilating air is used air. European Patent Publication EP 0,301,607 discloses a device and a method for an open loop and closed loop control of the ventilation of an enclosed pressurized space in such a manner that the pressure as well as the carbon dioxide concentration is maintained at a determined level within the enclosed space. For this purpose a pressure sensor measures the pressure level to provide an actual pressure value signal and a carbon dioxide sensor measures the carbon dioxide concentration in the enclosed space to provide an actual CO.sub.2 value signal. A respective open/closed loop control device monitors the actually measured values and compares the actually measured values with a respective rated value to provide corresponding control signals.
The result of this comparing provides control signals for controlling the supply of pressurized fresh air and thus the pressure level in the enclosed aircraft body. The fresh air is drawn from the outside of the enclosed body. The outside fresh air is mixed with a portion of the used air from the enclosed space and the mixed air is again introduced. Thus, the pressure and the carbon dioxide concentration is automatically maintained at a predetermined level depending on the proportions of used and fresh air in the recirculated air mixture. In the just described conventional solution the ventilation of the cabin is performed only with a closed and open loop control based on the carbon dioxide concentration and on the pressure in the enclosed space, whereby both parameters are automatically modified in dependence on one another and in accordance with a predetermined level. The conventional method does not permit feeding a desirably tempered and clean conditioned air into the cabin because this known method does not use any further treatment of a portion of the used air with a view to removing therefrom the above mentioned disease carriers, odors and other contaminations. The known method also forgoes feeding into the cabin, air that has a comfortable temperature.
German Patent Publication DE 865,358 discloses a further solution for an open and closed loop control of the ventilation of an enclosed space. An air circulator feeds with an air shower a mixture of withdrawn and fresh air into the enclosed space. The supply of fresh air which is sucked off from outside the enclosed space, is controlled in open and closed loop fashion through a valve in dependence on the monitored carbon dioxide concentration. The control is performed by a carbon dioxide control device connected to a carbon dioxide sensor to which the control responds. The CO.sub.2 sensor monitors the carbon dioxide concentration in the enclosed space. The known solution does not take into account any aspects of a pressure and temperature open loop and closed loop control. It does not involve any removal of excess heat which may possibly be present in the enclosed space nor does it remove disease carriers, odors, and other contamina tions from the cabin air that is being recycled.